Exhaust gas recirculation (EGR) may be used to increase an engine's fuel efficiency and reduce emissions. This is achieved by recirculating exhaust gas into the intake manifold for combination with ambient air before delivery to the combustion chamber. In systems utilizing a turbocharger, exhaust gas can be recirculated via a high-pressure system (HP-EGR) or a low-pressure system (LP-HGR). In HP-EGR systems the exhaust may have an outlet upstream of a turbine and an intake downstream of the compressor. HP-EGR systems allow a steady stream of gas in enter the intake system due to a higher pressure differential between the exhaust system and the intake manifold during non-boosted conditions; however, exhaust soot can accumulate or un-burned fuel can condense within the EGR or intake system causing engine degradation. LP-EGR systems couple an exhaust outlet downstream of a turbine to an inlet upstream of a compressor. By this method, exhaust gas can be purified by a particulate or other emission control system prior to recirculation into the intake system, lessening the soot content and the resulting build up within the engine system. However, in LP-EGR systems, exhaust gas traverses a substantial length of the vehicle before recirculating into the intake system, contributing to a number of problems within the EGR system.
During some conditions, pressure within an intake (MAP) is lower than pressure within the exhaust system. Intake compressors, exhaust turbines, and exhaust mufflers may each contribute to the pressure differential between the systems. However, pressure losses increase with increased LP-EGR length and in some long path LP-EGR systems, EGR flow cannot be maintained via the inherent pressure differential within the system. Back pressure valves may be incorporated into LP-EGR systems to create a sufficient pressure differential between the intake and exhaust system. However, the degradation of the additional valve component can disable the entire LP-EGR system. Further, resonance within the EGR system and intake resulting from this back pressure valve can create auditory disturbances for the driver and vibrations within the EGR that can lead to mechanical failures.
Increased EGR path length also causes increased feedback delays so that systems regulating recirculation in response to a current engine load may experience precision losses. Further, increased path length of the LP-EGR pipe increases production cost and vehicle weight and consumes limited under-carriage space.
The inventors, having recognized the above issues, provide various LP-EGR systems using a shorter EGR path, reducing the reliance on a back-pressure valve. In one example, the engine may be configured so that an exhaust pipe, with an initial flow direction towards the rear of the vehicle, turns so that it redirects gas towards the front of the vehicle. By introducing this turn in the exhaust pipe, exhaust gas is routed back toward the front of the vehicle where the intake system is located, relocating the turbine and tailpipes from the back of the vehicle to the front of the vehicle nearer the compressor.
The disclosed arrangement shortens the length of the EGR pipe, thus reducing pressure losses to such an extent that sufficient pressure can be generated by the muffler to sustain recirculation. The forward disposed exhaust system also lessens the weight of the vehicle by removing an excessively long EGR pipe and lessens the response time of recirculation for systems that meter recirculation in response to operating conditions or load considerations. Further, by placing the tail pipe in the front of the vehicle, heated exhaust gas may be directed toward the ground and may transfer heat to ice or snow present on the road prior to contact with the tires thus increasing tire traction of front tires and improving drivability.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.